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Phylogenetic tree based on the nucleotide sequences of HA fragments (nucleotides 98 to 836) of influenza B viruses. Reference strains are indicated by bold letters, and the rest represent all 49 clinical isolates studied. Abbreviations: Victoria 00, B/Victoria/504/00; Yamagata 88, B/Yamagata/16/88; HK1351, B/Hong Kong 1351/02; HK330, B/Hong Kong/330/01; Victoria 87, B/Victoria/2/87.
